A detection device for detecting a specific functional group existing in a fluid is expected to be widely used in the field of biosensors detecting amino acids or DNA molecules in a body fluid.
Lately, Information Technology (IT) and Nanotechnology (NT), which have hitherto been separately improved, have been fused together, thereby rapidly developing a new technological base on the basis of Biology Technology (BT). In particular, research on a biosensor for detecting protein in blood is actively being conducted in the field of nano-biochip which is one of NT-BT fusion technologies.
In the field of nano-biochip, various methods for detecting, analyzing and quantifying a specific biomaterial are being developed. A representative one of the methods detects a specific biomaterial by fluorescence labeling. The fluorescence labeling method is frequently employed in currently used DNA chips.
However, the fluorescence labeling method requires an additional step of bio-chemically preparing a sample for measurement such as blood and saliva to detect a specific biomaterial, and thus it is difficult to apply various materials to the method. For example, when protein is labeled, about 50% of functional protein is inactivated in an unspecific labeling process. Therefore, only a very small amount of analyte can be appropriately used for a purpose.
For this reason, biosensors have begun to be proposed which have improved sensitivity and reproducibility and can be mass-produced through a semiconductor process. As an example, a high-sensitivity biosensor capable of detecting a specific material using a Si-nanowire fabricated through Chemical Vapor Deposition (CVD) has been widely researched according to a bottom-up method for several recent years. However, lately, a Si-nanowire biosensor which can be mass-produced in a top-down method using a current industrial Complementary Metal-Oxide Semiconductor (CMOS), easily implemented and has ensured reproducibility is being widely researched. In addition, many research results on an Ion-Sensitive Field Effect Transistor (ISFET) that is fabricated using a CMOS process as is and has the same structure as an FET, have been reported.
An ISFET is similar to a nanowire biosensor in that target molecules in solution react with probe molecules of a sensor to increase surface charges and thereby conductivity of the sensor is changed. On the other hand, an ISFET has a characteristic structure of a general FET, a gate voltage is determined by target molecules adsorbed on the upper part of a gate, and the gate voltage follows a pattern of an operation characteristic curve of the ISFET.
However, a changed amount of charge caused by a reaction between probe molecules and target molecules cannot remarkably change the total gate voltage, and thus the sensitivity of the ISFET considerably deteriorates. Since pH concentration and salinity of human blood directly affecting the amount of charge of target molecules vary according to persons, it is preferable to dilute blood with much reference solution. Therefore, to remove dependence on conditions of serum, the serum must be diluted with reference solution, and thus a high-sensitivity sensor may be further required.
In addition, it is not easy to dilute blood extracted from human body with reference solution after quantifying a small amount of blood. When a dilution ratio is one over several hundreds of thousands, an extremely small amount of blood must be quantified and diluted with reference solution, or blood must be diluted with a very large amount of reference solution. This is an unrealistic and very difficult technical problem.